Provide Array of permitted values for an option.

[joshuapinter]

I have an .option() that is only allowed to be one of "all", "debug" or "none".

I'd like an easy way to pass an Array to an option() and have Commander automatically check that the value passed by the user is one of the permitted values.

Something like this:

.option('-t, --target <target>', 'Specifies the target.', ["all", "debug", "none"])

Also including the permitted values in the help output could be useful, provided it's not a very large Array.

I'd gladly do the PR if I can get a response from @tj or a collaborator that this is useful.

Thanks!!

[tmiddlet2666]

I second this, Would be great to be able to do this and validate options.

[shadowspawn]

1. The .option call is quite flexible already and it is not easy to add more functionality to the current signature. I am wondering about allowing building options to make it possible to add less common functionality without complicating the existing usage. See Feature Request: ability to hide options #1106 (comment)

2. As a different approach, I have been wondering if there could be a collection of validators available from Commander to use as custom option processing functions, but my first attempts were a bit clumsy due to option name not being easily available for error messages. For an example of a simple bring-your-own validator for an array of expected values: When providing custom function for options, requiredOption don't work #1130 (comment)

(I suspect that neither of these are as "easy" as OP had in mind when said "I'd like an easy way to pass an Array to an option() and have Commander automatically check that the value passed by the user is one of the permitted values."! See next two comments for what code could look like.)

[shadowspawn]

I have been wondering about the syntax and here is one approach, fluent (chaining) calls on Option object like with Command object:

program
   .addOption(new Option('-t, --target <target>', 'Specifies the target (all | debug | none).')
      .valueIncludedIn(["all", "debug", "none"])
   )
);

This style might be used for other enhancements for options, like:

program
   .addOption(new Option('-f, --devFeature <feature-flag>').hidden());

[shadowspawn]

And another approach, convenience routines for custom option processing with existing api:

program
   .option('-t, --target <target>', 
      'Specifies the target (all | debug | none).', 
      OptionValue.includedIn(["all", "debug", "none"])()
   )

This style might be used for adding other custom option processing including from the examples, like:

program
   .option('-t, --target <target>', 
      'Specifies the target(s), comma separated', 
      OptionValue.csv
   )

[shadowspawn]

Related link from #215 (comment)

Python argparser has choices for restricting allowed values: https://docs.python.org/3/library/argparse.html#choices

Yargs has choices too.